The present invention relates to the field of drill bits for drilling in rock and other earthen formations. More particularly, the present invention relates to center vacuum drill bits as are most useful in drilling blast holes and ceiling anchor holes in coal mines.
The well known prior art center vacuum drill bit is shown in FIG. 1. The center vacuum drill bit 2 comprises a generally flat insert of hard wear resistant material 4, usually cemented carbide, situated in a body 8. The insert is typically brazed 6 to the body.
While this prior art drill bit has performed well, it would be desirable to improve the construction of the drill bit. One improvement would be to make the insert readily releasable from the body. This improvement is of importance for three reasons. The first is that the worn insert can be easily removed for salvage. The second is that the body can be reused when a new insert is situated in the body. The third, and possibly most important, reason is that all brazing problems, as are well known to those skilled in the art, can be effectively eliminated.
Releasable inserts in rock drills are illustrated in U.S. Pat. Nos. 2,575,239 and 3,878,905. However, since these rock drills require that the insert be held in the center, the inserts must necessarily be unsuitable for use in center vacuum drill bits.
Another type of releasable insert is manufactured by Alaskaug Inc., Cincinnati, Ohio. This releasable insert is used in a blast hole auger bit. Again, the type of arrangement manufactured would not be suitable for use as a center vacuum drill bit.
Accordingly, it is an object of the invention to have a releasable insert suitable for use with a center vacuum drill bit.
It is another object of the invention to have a center vacuum drill bit that is easily and economically manufactured.